1. Field of the Invention
The present invention relates to a fuel cell.
2. Discussion of the Background
For example, in a solid polymer electrolyte fuel cell, a membrane-electrode assembly (MEA) is sandwiched between a pair of separators, the membrane-electrode assembly including a polymer electrolyte membrane formed of a polymer ion exchange membrane, and the anode and cathode electrodes that are disposed on the respective sides of the polymer electrolyte membrane. In general, a plurality of fuel cells is stacked together to form a fuel cell stack, and in addition to stationary use, the fuel cell stack is incorporated into a fuel cell vehicle to be used as an in-vehicle fuel cell system.
The above-mentioned fuel cell is provided with a fuel gas passage for passing a fuel gas to the anode electrode (hereinafter, referred to as a reactant gas passage), and an oxidant gas passage for passing an oxidant gas to the cathode electrode (hereinafter, also referred to as a reactant gas passage), within the respective surfaces of the separators. In addition, a cooling medium passage for passing therethrough a cooling medium is provided in the longitudinal direction of the separators, for each power generation cell or for each set of a plurality of power generation cells.
In this type of fuel cell, in order to secure a favorable ionic conduction property, the electrolyte membrane needs to be maintained at a certain water content. For this reason, a system is employed, in which an oxidant gas (for example, air) and a fuel gas (for example, hydrogen gas) as reactant gases are humidified and supplied to the fuel cells.
When the reactant gases are humidified, water contained in the reaction gases used for the humidification may be liquefied without being absorbed in the electrolyte membrane, and may stay in the reactant gas passages. On the other hand, in the fuel cell, water is produced in the cathode electrode by the power generation reaction, while the product water diffuses back into the anode electrode via the electrolyte membrane. Consequently, at the lower end, in the direction of gravity, of the reactant gas passage, water content tends to condense and remain due to the effect of gravity, and thus flooding of the condensed water may occur.
As a fuel cell configured to efficiently drain product water while effectively discharging exhausted gas, there is known, for example, the solid polymer electrolyte fuel cell disclosed in Japanese Patent No. 3123992. As shown in FIG. 11, the fuel cell includes a frame 1. A cell 2 and a cathode-side passage substrate 3 are installed on one surface of the frame 1, while an anode-side passage substrate 4 is installed on the other surface of the frame 1.
The cell 2 includes a solid polymer electrolyte 2a which is sandwiched between a cathode 2b and an anode 2c. In the cathode-side passage substrate 3, a plurality of cathode-side passages 3a are formed, while in the anode-side passage substrate 4, a plurality of anode-side passages 4a are formed.
On the upstream side of the frame 1, there are formed a pair of water supply manifold holes 5a, a groove hole 5b through which the water supply manifold holes 5a communicate with the anode-side passages 4a, a pair of fuel gas supply manifold holes 6a, and a groove hole 6b through which the fuel gas supply manifold holes 6a communicate with the anode-side passages 4a. On the downstream side of the frame 1, there are formed a pair of fuel gas discharge manifold holes 7a, a groove hole 7b through which the fuel gas discharge manifold holes 7a communicate with the anode-side passages 4a, a pair of water discharge manifold holes 8a, and a groove hole 8b through which the water discharge manifold holes 8a communicate with the anode-side passages 4a. 
Then unreacted fuel gas which has passed through the anode-side passages 4a is discharged from the groove hole 7b to the outside of the battery through the fuel gas discharge manifold holes 7a, while the water which has passed through the anode-side passages 4a is discharged from the groove hole 8b to the outside of the battery through the water discharge manifold holes 8a. 